The acl_add_perm() function adds the permission
contained in the argument perm to the
permission set referred to by the argument
permset_d. An attempt to add a permission
that is already contained in the permission set is not considered an error.

Any existing descriptors that refer to
permset_d continue to refer to that
permission set.

RETURN
VALUE

The acl_add_perm() function returns the
value 0 if successful; otherwise the value -1 is returned and
the global variable errno is set to indicate
the error.

ERRORS

If any of the following conditions occur, the
acl_add_perm() function returns
-1 and sets errno to
the corresponding value:

[EINVAL]

The argument permset_d is
not a valid descriptor for a permission set within an ACL entry.